The waiting is over: Firefox 31.8.0 ESR Beta 5 for OS/2 was just released yesterday. The delay was caused by latest fixes for the open file dialog. The other changes that took place you can read in the post about the 31 ESR build.
Compared to the alpha build this release needs the libkai 1.1.4 runtime to get this build starting.

Changes in this release:

Update Firefox to version 31.8.0 ESR.

Put back all OS/2 code that was removed by the Mozilla team between
versions 24 and 31 to bring Firefox back to life.

Another major OS/2 USB driver update was just recently released on 06/10/2015. It contains refreshed host controller drivers and the new and updated usbmsd.add which is currently being worked on. The list below shows all the included driver files in more detail.

Wim has just released his own version of usbresmg.sys and the usbcalls.dll lib on 07/17/15. This version is the 4th (beta) release with a new Rexx interface and it comes with a help file usbrexx.inf which contains more information how to use the new rexx functions.